A strong desire for increased automation in the workplace, and a desire to increase the use of animated figures depicting animals, humans or other characters in entertainment and other situations, along with an increased ability to control such mechanical manipulators has led to substantial efforts in the development of robotics. As a result, significant advances have occurred in many aspects of robotics.
Perhaps the most widely used controlled component in robotic systems is a mechanical manipulator, that portion of a robot often used in connection with an end effect or to change the position or orientation of selected objects engaged by that manipulator. In many instances, such mechanical manipulators are desired to have capabilities similar to those of the human wrist or shoulder, that is, exhibiting two (or in some instances, more) degrees of freedom of motion.
Although a number of such mechanical manipulators have been developed which to a greater or lesser degree achieve some of these desires therefor, most have been relatively complicated devices requiring complicated components and difficult assembly procedures or both. Many, in addition, represent compromises in having relatively limited range, or singularities within the ranges, or other limitations in performance. Thus, there is a strong desire for a mechanical manipulator which can, under control of the user, position objects anywhere over at least a hemispherical surface without any singularities in the operation of the device in this range, and which can be made both reliably and inexpensively.
One such mechanical manipulator meeting this desire comprises a base support, a pivot holder and a plurality of pivoting links. The pivoting links are rotatably coupled to both the base support so as to be arrayed by rotational axis radially thereabout and to members of the pivot holder to rotate about axes which extend in different directions for each of these rotatable couplings in a link typically in accord with specific geometrical arrangements, and in different directions from similar axes in another of such links. The pivot holder is linked with a second plurality of pivoting links to a manipulable support. Such systems can incorporate a variety of force imparting members to control movements of various ones of the pivoting links or pivot holder members with as few as two being required. Pivot holder members having hinged portions with one portion rotatably connected to a first plurality pivoting link and the other portion rotatably connected to a second plurality pivoting link provides a capability for controlling the separation between the base and manipulable supports, but requires an actuator for each first plurality pivoting link and has its manipulable support positioned less precisely.
Another manipulable support meeting this desire comprises a base support, a pivot holder with hinged members and three pivoting links. The pivoting links are rotatably coupled to both the base support, but this time to be arrayed by axis more or less tangentially thereabout, and to members of the pivot holder to rotate about axes which extend in different directions for each of these rotatable couplings in a link typically in accord with specific geometrical arrangements, and in different directions from similar axes in another of such links. The pivot holder is linked with another three pivoting links to a manipulable support. Such systems can incorporate a variety of force imparting members to control movements of various ones of the pivoting links or pivot holder members with three being required.
This latter mechanical manipulator has a stronger construction than the former in having the three pivoting links connected to the base support with the rotation axis for each positioned tangentially thereto rather than being more or less cantilevered radially therefrom. However, there is much less vertical support provided to loads on the manipulable support positioned at relatively extreme angles with respect to vertical in some radial positions. In operation, the operation of any one actuator can not be controlled independently from the others because of the unavoidable coupling between the three pivoting links.
Still, such mechanical manipulators having only three pairs of pivoting links rotatably coupled to the pivot holder members have a further advantage in having fewer pivoting links therein as this can tend to reduce the possibilities of interference between manipulator components in the course of performing various manipulator motions directed by the actuators. This reduced opportunity for component interference during manipulator motions can allow the manipulable support, and any objects affixed thereto, to be positioned over a wider range of positions by the actuators or to provide a more compact manipulator, or both.
Yet, the reduced support provided to loads on a manipulable support in the manipulator, at least when positioned at relatively extreme angles with respect to vertical in some radial positions, remains a problem. This problem arises because the pivoting links, the rotary joints, the actuators, and even the transducers used in measuring certain variables in the manipulator during use for the manipulator control system, are compliant, or flexible, under applied loads. This yielding makes precision positioning of the manipulable support more difficult. The problem is further compounded by nonlinear effects such as joint backlash. Thus, there is a desire for a mechanical manipulator that is economical and strongly constructed to provide a wide range of output position including being capable of providing relatively good vertical support for output loads even at extreme angular positions.